Usually, an HIV test doesn't test for presence of the virus itself; it tests for the antibodies your immune system develops in response to infection. The "window period" is the span of time between contracting the virus and the presence of detectable antibodies, which can be up to 6 months in some cases (though it's usually shorter). During this period, a person will test negative for HIV even though he or she is infected with the virus (and, worse, is contagious).
Newer tests have been developed that test for presence of the virus's RNA, shortening the window period to about 21 days (if I recall correctly), but they are more expensive and much, much less widespread.
thanks for the explanation. it worries me that anyone thinks this is common knowledge amongst a more-or-less programmer community. It worries me even more that perhaps it is, and I'm just ignorant.
An additional piece of information- you're approximately 4,000% more likely to transmit HIV during this early stage infection because of this high viral load. Some research estimates as much as 50% of all new infections come from people in this early infectious window.
Here is an excellent video that explain in detail this that in the early stages it is much more contagious http://www.ted.com/talks/elizabeth_pisani_sex_drugs_and_hiv_... and others IMPORTANT commonly unknow details that change totally how to fight to the virus.
Any time I see a comment like yours, the correct response to your question is almost always, "It's a system problem." If we aren't effectively disseminating knowledge about an important public health risk, we're not putting ourselves in a winning position.
This was taught in my school system, but not in such depth. They focused on prevention, rather than recognition, and we had to rely on old faithful Wikipedia to tell us the rest.
I only learned about it the first time I got tested. If this is the case among most people, a self-test like this could be dangerous in that a lot of people who've never been tested would be likely to start using it. If I'm abnormal, though, I'm curious where most people know it from.
Newer tests have been developed that test for presence of the virus's RNA, shortening the window period to about 21 days (if I recall correctly), but they are more expensive and much, much less widespread.